This invention relates to an improved arrangement of an axial-flow cooling fan attached to an internal combustion engine.
In recent automotive engines, miscellaneous equipments and optional accessories are attached to an output shaft on the side of a fan. For example, within a space between a radiator and a fan, many accessories such as a condenser of airconditioner, inter-cooler and oil cooler are disposed. Further, within a space between a fan and an engine housing, an alternator (generator), compressor of air conditioner, super charger and and other accessories are closely disposed. This results in an increase of air flow resistance around a cooling fan.
Fan blades of a fan receive upstream air and discharge it toward an engine housing in a pressurized condition. Since the pressure varies depending upon a distance from a central axis of the fan, some areas in upstream side of the fan holds a relatively low pressure than in the downstream side. Due to this imbalance of pressure, some of the air flow having passed through the fan blades turn back toward the central axis of the fan. This counter current flow gives rise to a loss of engine power.
In Japanese Patent Public Disclosure No. 176499/1984 (SHO 59-176499), there is disclosed a cooling apparatus wherein a fan boss having a taper section is utilized for preventing air flow from peeling off. Although this arrangement intends to improve an efficiency of the axial-flow fan, the width of the fan boss is so small that the effect is not so distinguished as expected.
In Japanese Utility Model Public Disclosure No. 75199/1982 (SHO 57-75199), there is disclosed a cooling fan wherein a frust-conical ring is disposed at a downstream side of the fan. Although this frust-conical ring can extend a diameter of air flow, the diameter of the ring is so small that the effect is not so distinguished as expected.